Photographic inhibitor releasing developers



United States Patent 3,297,445 PHOTOGRAPHIC INHIBITOR RELEASING DEVELOPERS Frederick C. Duennehier and James T. Kofron, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Apr. 1, 1963, Ser. No. 269,731

Claims. (Cl. 96-95) This invention concerns inhibitor releasing developers and more particularly photographic emulsions containing such developers.

It is well-known in the photographic art to employ developing agents in the photographic emulsion. These developing agents can be activated to provide development of the latent image and in some instances to harden or tan the colloid containing the silver halide in the exposed regions whioh will subsequently form relief images after the unhardened images have been removed. However, the presence of the developing agent in the photographic emulsion may have an adverse effect on the keeping qualities of the emulsion resulting in an overall hard ening of the emulsion or fogging. In addition, the developing action carried on by the use of an alkaline agent which initiates development may result in fog or other adverse results. Therefore, it has been desirable to incorporate a developing inhibiting agent along with the developer which would reduce fog and improve the keeping characteristics of the photographic emulsion. Preferably, such an inhibtor would also result in inactivating the developer or keeping it in an inactive state until such time that it is needed for carrying out development following exposure.

Hydraquinone has been combined with various materials in the prior art for use as developers or for incorpor ating in photographic emulsions. For instance, certain compounds of this type have been used wherein it is desired to eliminate and minimize the need for washing or stabilizing operations in liquid photographic baths subsequent to the formation of the silver image, for instance in the diffusion transfer systems, particularly where prints are desired from a silver halide emulsion which has been substantially underexposed in relation to its ASA exposure index. However, these prior art hydroquinone derivatives do not provide inhibitors at the site of development or produce the desired effect of reducing contrast at no loss of speed.

We have found substituted iodohydroquinones which, upon activation, result in free hydroquinone and which also release iodine at or near the site of development. This iodine release results in reduced contrast and increased edge eflects with little or no loss in speeds.

One object of this invention is to provide inhibitor releasing developers. Another object is to provide photographic emulsions containing inhibitor releasing developers. A further object is to provide developer containing emulsions having reduced contrast and increased edge eifects with little or no loss in effective speed. A further object is to provide a development inhibitor (i.e. iodine) in chemical combination with a developing agent which releases the inhibitor at or near the site of development. A still further object is to :provide iodo substituted hydroquinones. Another object is to provide new inhibitor releasing compounds that can be used in liquid developing solutions. Other objects will be apparent from the following disclosure.

The hydroquinone developers which are useful in our invention are preferably prepared by reacting a phenol with iodine and hydrogen peroxide. The iodobenzoquinone thus formed is then reduced to the corresponding iodohydroquinone.

The iodo derivatives of hydroquinone are preferably incorporated in the photographic emulsion by forming a dispersion in a high boiling crystalloidal solvent of the type described in lelley et al., US. Patent 2,322,027. These developers may be substituted in an amount of 5 to mol percent depending upon the particular compound and the desired decrease in contrast.

Compounds falling within the scope of our invention are illustrated by the following general formula:

wherein R R R and R each represents a hydrogen atom, an iodine atom, an alkyl group (for example an alkyl group having about l-20 carbon atoms, such as methyl, butyl, octyl, decyl, tridecyl, eicosyl, etc.), OH, amine, an aryl group (for example an aryl group such as phenyl, tolyl, xylyl, etc.). R and R each represents a hydrogen atom, or any alkaline splittable masking group, for example, a group such as, acetyl, mono-, di-, or trichloroacetyl, mono-, di-, or trifluoroacetyl, perfluoroacyl (e.g., butyryl), pyruvyl, alkoxalyl, nitrobenzoyl, cyanobenzoyl, etc.

The substituents on the hydroquinone ring are not critical and may be the same or different. At least one of the substituents, R R R 0r R must be iodine and one of the other substituents, R R R or R must be a group other than hydrogen. Preferably, the substituted hydroquinone will be an active developer. However, the activity of the substituted hydroquinone will depend upon its desired use and may be negligible.

The release of iodine is facilitated by the action of sulfite ions on the quinone as shown in the following equation:

replacement reaction.

OH (H) I I! l S03:

I OH 0 OH The presence in the compound of an alkyl substituent containing 10-20 carbon atoms prevents the molecule from diffusing when it is incorporated in a multilayer system. In instances where diffusibility is desirable, the alkyl groups should be kept small, i.e. below 8 carbon atoms.

3 The following compounds are typical of those useful in our invention:

2-iodo-5-pentadecyl hydroquinone 2-iodo-3-methyl-6-isopropylhydroquinone I OH 3,S-dimethyl-Z-iodo-6-dodecylhydroquinone O H; C H3 2-iodo-3,6-dimethylhydroquinone I -CH3 (VII) 2,6 -diiodohydroquinonebischloroacetate OCOCHzCl I O CHCH Cl These compounds can be used either in developer solution (i.e., in the case of the diffusible compounds, eg Compounds II and III above) or by incorporation into the emulsion layers at the time of coating.

The iodohydroquinones useful in this invention may be synthesized as shown by the following typical prepara- 4 tion of 6-iodo-2,3,S-trimethylhydroquinone, Compound III.

To a solution of 30 g. of 6-iodo-2,3,5-trimethyl-pbenzoquinone (Intermediate A below) in one liter of diethyl ether was added with stirring a solution of 50 g. of sodium hydrosulfite (Na S O in 400 ml. of water. After two hours, the colorless ether layer was separated from the aqueous phase, washed with two ml. of water, dried over sodium sulfate and concentrated in vacuo. The solid residue was recrystallized from Eastman No. 513 ligroine (B.P. 6675 C.), yielding the product, M.P. 106-107 C.

Intermediate A .6-i0d0-2,3 ,5 -lrimetlz yZ-p-benzoquinone To a solution of 41g. of 2,3,5-trimethylphenol and 75 g. of iodine in 600 ml. of ethyl alcohol was added at 60 C. with stirring over a period of two hours, 100 ml. of 35 percent of hydrogen peroxide. The mixture was stirred at room temperature overnight, after which time it was cooled to 5 C. The product which separated was collected and dried, M.P. 74-75 C.

The following examples are intended to illustrate our invention but not to limit it in any way:

EXAMPLE I 2-iodo-5-pentadecy1 hydroquinone, Compound I, was used in a single layer silver bromoiodide emulsion for the purpose of reducing the contrast of the image within the layer as follows:

A dispersion was prepared by adding a solution of 0.5 g. of 1-(2,4,6-trichlorophenyl)-3-[3-(2,4-di-amylphenoxyacetamido)benzamido]-5-pyrazolone and 0.1 g. of Compound I in 0.26 ml. of tricresyl phosphate plus 3 ml. of ethyl acetate to a mixture of 22 ml. of 10 percent bone gelatin and 2 ml. of 5 percent propylated naphthalene sulfonate. This mixture was milled 5 times in a colloid mill, chilled, and dried. A solution of 1.83 g. of this dried dispersion in 21 ml. of water containing 7.5 percent solution of saponin in water was mixed with 13 ml. of medium speed silver bromoiodide emulsion containing .250 g. of silver, and coated on film support (Coating A). Two control coatings were prepared; Coating B similar to A but without the inhibitor-releasing hydroquinone, and Coating C similar to A but with 2-methyl-5-octadecylhydroquinone replacing the inhibitor-releasing hydroquinone When these coatings were given sensitometric exposures and processed in a negative color process, Coating A showed about 10 percent reduction in contrast compared to the controls at equal speed. Traces of line exposures processed similarly showed improved sharpness in Coating A but not in the controls. Both of these results can be attributed to imagewise release of inhibitor in coating A.

Process at 70 F.: Min. Color developer 12 Kodak F-5 fix 5 Wash 5 Bleach (potassium bromideferricyanide) 8 Wash 3 Kodak F-S fix 5 Wash 10 Color developer: G.

Calgon (sodium hexametaphosphate) 1.0 Sodium sulfite (desiccated) 4.0

Sodium carbonate monohydrate 20.0 Sodium bromide 1.7 4-amino-N,N-diethyl-3-methyl-aniline-HCl 3.0 Water to make 1 liter.

EXAMPLE II Using coatings similar to those prepared for Example I and a low potential developer containing 22.5 g./l. of sodium sulfite, 11.6 g./l. of sodium hydroquinone monosulfonate, 17.0 g./l. of sodium carbonate, and 1.5 g./l. of potassium bromide at pH 12.0, a silver image was developed which showed sharper images when Compound I was present in the coatings.

EXAMPLE III When a developer containing 6.0 g./l. of p-methylaminophenol sulfate, 4.0 g./l. of hydroquinone, 6.6 g./l. of 2,6-diiodohydroquinone (Compound II), 30 g./l. of sodium sulfite, 35 g./1. of sodium carbonate, and 1 g./l. of potassium bromide was used to process exposed high speed, coarse grain silver bromoiodide emulsion, edge effects were produced which showed both higher density at the edge of a sharp line as well as fog repression in the immediately adjacent region. Under similar conditions and with a check developer as above but containing 6 g./l. of hydroquinone with no iodo compound, sharpness improvement was negligible and percent higher contrast was obtained at equal speed.

EXAMPLE IV When the check developer of Example III was used to process exposed silver bromoiodide emulsions sensitive to iodide ion, no edge effects were noted. When a similar developer in which 0.4 g./l. of hydroquinone was replaced with 0.9 g./l. of 2-iodo-3,5-6trimethylhydroquinone (Compound III) was used, repression of fog and image development were noted and traces of lines showed edge effects which improved sharpness.

EXAMPLE V A coating was prepared using emulsions similar to those of Example IV by coating a blue sensitized layer containing yellow coupler over a red sensitized layer containing cyan coupler with an intervening layer containing yellow colloidal silver. Using an Ektachrome reversal process with a first developer like the check developer of Example 111, no masking effect was noted in the cyan layer as a function of exposure in the blue sensitive top layer. When the developer of Example IV containing 0.9 g./l. of 2-iodo-3,5,6-trimethyl hydroquinone (Compound III) was used as a first developer, development in the cyan layer was partially attenuated as a function of exposure and development in the blue sensitive layer with the result that a desirable interimage or masking effect was introduced. Such an effect is valuable for improving color rendition by correcting for unwanted absorptions in image dyes.

EXAMPLE VI Using a coating and process as in Example V but replacing the 0.9 g./l. of 2-iodo-3,5,6-trirnethylhydroquinone (Compound III) with 1.0 g./l. of 2-iodo-3- methyl-6-isopropylhydroquinone (Compound IV) a similar desirable masking effect was obtained.

The iodo developer compounds of our invention can be incorporated in an ordinary photographic silver halide emulsion, or colloidal dispersion of a water-permeable hydrophilic colloid suitable for preparing an undercoat or an overcoat for such silver halide emulsion, by mixing a solution or dispersion of the developer compound with the silver halide emulsion, or dispersion of hydrophilic colloid, prior to coating. For example, an iodo developer can be made up as an oil dispersion by stirring a solution of 10 grams of the iodo developing agent into 40 grams of warm tricresyl phosphate, and then mixing this solution with 100 grams of a 10 percent aqueous gelatin solution containing 10 ccs. of a 5 percent aqueous solution of an alkylnaphthylene sodium sulfonate wetting agent. The resulting dispersion can then be homogenized by passing for 5 times through a colloid mill to produce a homogeneous colloid dispersion. Solvents other than tricresyl phosphate can be employed, including any of the crystalloidal compounds described in Jelley and Vittum US. Patent 2,322,027, issued June 15, 1943. The resulting colloidal dispersion can then be added to an ordinary silver halide emulsion, or a dispersion of a water-permeable hydrophilic colloid, adapted for preparation of an undercoat or overcoat for such silver halide emulsion.

Instead of adding the oil dispersion" directly to the liquid silver halide emulsion or colloidal dispersion, it can be dried for storage purposes and then be recoustituted for use by merely mixing with water.

The iodo developing agents of our invention can be adapted for addition to a liquid silver halide emulsion or colloidal dispersion by other means as well. Suitable methods will depend largely upon the solubility characteristics, particularly in water or polar solvents, of the particular precursors in question.

After addition of the dispersion or solution of the iodo developing agent substance to the liquid emulsion or colloidal dispersion, the mixture is stirred to assure uniform results, or passed through a blending device, such as a colloid mill or Waring Blendor. A uniform coating can then be made on a suitable support and the coating dried. Suitable supports comprise any of the well known supporting materials, such as cellulose ester film base (erg. cellulose acetate, cellulose nitrate, cellulose acetate butyrate, cellulose acetate propionate, etc.), polyethylene, polypropylene, polystyrene, polyethylene terephthalate and other polyesters, paper, polycarbonates, etc.

The photographic elements of our invention comprising a photographic iodo development agent either in the photographic silver halide emulsion layer, or layer contiguous thereto, or both, can then be exposed to an original or negative and developed by merely treating the exposed emulsion layer with an alkaline activator bath. Typical activator baths comprise, for example, an aqueous solution of an alkaline material, such as sodium carbonate, sodium hydroxide, potassium carbonate, potassium hydroxide, mixtures of sodium hydroxide and sodium sulfite, etc. Suitable baths can comprise, for example, an aqueous solution containing about 1 percent sodium hydroxide and 5 percent sodium sulfite. A bath of the latter type is quite suitable for developing an exposed emulsion layer in about 30 seconds when the activator bath is at about 68 F. Modifications can easily be made in the activator baths without departing from the spirit and scope of the invention. For example, an aqueous solution comprising about 4 percent of sodium carbonate and 5 percent of sodium sulfite produces development in about 30 seconds at 68 F. Another aqueous activator solution comprising 2 percent sodium hydroxide and 5 percent sodium sulfite produces useful photographic images in a few seconds when heated at F. Particularly useful activator solutions have a pH of at least about 9.0 and preferably of at least about 10.5.

The activator solutions of the present invention can be applied to an exposed photographic element in any number of known ways, such as by dipping, spraying, or other suitable surface applications. If desired, a thickener can be added to the activator solution to increase the viscosity of the composition and make it more adaptable for continuous processing. Viscous compositions can then be removed by squeegeeing or water spraying. The photographic element can then be stabilized by conventional fixation or stabilization, such as by sodium thiosulfate.

The concentration of the iodo developers used in our invention will vary, chemical compound involved and the location of the compound within the photographic element. That is, if the iodo developer is incorporated within the silver halide emulsion undergoing development, it may be desirable to use a somewhat different concentration than would be used if the iodo developers were incorporated in a layer contiguous to the photographic silver halide emulsion. A useful concentration of iodo developer for incorporation in the emulsion is from about 0.01 to 4.0 moles per mole of silver halide. A particularly useful range is from about 0.1 to 2.0 moles per mole of silver depending upon the particular halide, with especially useful results 'being obtained within the range of about 0.4 to 1.0 mole per mole of silver halide. For incorporation in a layer contiguous to the silver halide emulsion layer, somewhat larger concentrations of iodo developer can be tolerated without adverse effects. A particularly useful effect of our invention is that even when incorporated within the silver halide emulsion, the iodo developers have little or no desensitizing effects. In many cases, this is not true where developing agents, per so, are incorporated within the silver halide emulsion layers.

Photographic silver halide emulsions useful in our invention comprise any of the ordinarily employed silver halide developing-out emulsions, such as, silver-chloride, -chlorobromide, -chloroiodide, -chlorobromoiodide, -bromide and -bromoiodide developing-out emulsions. Any of the conventionally employed water-permeable hydrophilic colloids can be employed in the silver halide emulsions, or in layers contiguous thereto. Typical waterpermeable hydrophilic colloids include gelatin, albumin, polyvinyl alcohol, agar agar, sodium alginate, hydrolyzed cellulose esters, hydrophilic polyvinyl copolymers, etc.

Photographic silver halide emulsions useful in our invention can also contain such addenda as chemical sensitizers, e.g. sulfur sensitizers (e.g. allyl thiocarbamate, thiourea, allyl isothiocyanate, cystine, etc.), various gold compounds (e.g. potassium chloroaurate, auric trichloride, etc.). (See U.S. Patents 2,540,085, 2,597,856 and 2,597,915, etc.)

Photographic silver halide emulsions useful in our invention can also be sensitized by other means, such as by alkylene oxide polymers, many of which are well known to those skilled in the photographic art. Typical polyalkylene oxide polymers include those of U.S. Patents 2,423,549 and 2,441,389.

The emulsions of the invention can also contain speedincreasing compounds of the quaternary ammonium type as described in U.S. Patents 2,271,623, issued February 3, 1942; 2,288,226, issued June 30, 1942; 2,334,864, issued November 23, 1943; or the thiopolymers as described in Graham et al., U.S. application Serial No. 779,839, filed December 12, 1958; and Dann et al., U.S. application Serial No. 779,874, filed December 12, 1958.

The emulsions may also be chemically sensitized with reducing agents such as stannous salts (Carroll U.S. Patent 2,487,850), polyamines such as diethylene triamine (Lowe and Jones U.S. Patent 2,518,698), polyamines such as spermine, (Lowe and Allen U.S. Patent 2,521,925), or bis-(fl-aminoethyl) sulfide and its water-soluble salts (Lowe and Jones U.S. Patent 2,521,926).

The emulsions may also be stabilized with the mercury compounds of Allen, Byers and Murray U.S. application Serial No. 319,611; Carroll and Murray U.S. application Serial No. 319,612; and Leubner and Murray U.S. application Serial No. 319,613, all filed November 8, 1952, now U.S. Patents 2,728,663, 2,728,664 and 2,728,665, respectively, granted December 27, 1955.

The addenda which we have described may be used in various kinds of photographic emulsions. In addition to being useful in X-ray and other nonoptically sensitized emulsions, they may also be used in orthochromatic, panchromatic, and infrared sensitive emulsions. They may be added to the emulsion before or after any sensitizing dyes which are used. The agents may be used in emulsions intended for color photography, for example, emulsions containing color-forming couplers or emulsions to be developed by solutions containing couplers or other color-generating materials, emulsions of the mixed-packet type, such as described in Godowsky, U.S. Patent 2,698,794, issued January 9, 1955; or emulsions of the mixed-grain type, such as described in Carroll and Hanson U.S. Patent 2,592,243.

It has been found that the development rate of the iodo developers above can be improved by adding an auxiliary developing agent either to the silver halide emulsion layer, or a hydrophilic layer contiguous thereto. Typical auxiliary developing agents include those described in the copending application Serial No. 134,014, filed August 5, 1961, of P. H. Stewart, G. E. Fallesen and J. W. Reeves, Jr. Typical auxiliary developing agents described in this application include 3-pyrazolidone compounds containing an alkyl (e.g. methyl, ethyl, etc.) or aryl substituent (e.g. phenyl, p-tolyl, etc.). In addition, such pyrazolidone developing agents can contain an acyl or acyloxy substituent which can be hydrolyzed from the 3-pyrazolidone compound by treatment with the above activator solutions to produce the desired auxiliary developing compound. Typical auxiliary developing agents include, for example, 1-phenyl-3-pyrazolidone, l-p-tolyl- S-pyrazolidone, 1-phenyl-5-methyl-3-pyrazolidone, l-acetamidophenyl-3-pyrazolidone, 3-acetoxy-1-phenyl-3-pyrazolidone (Enol ester), Z-(pyridinium acetyl)-l-phenyl 3-pyrazolidone chloride, 1-phenyl-4,4-dimethyl-3-pyrazolidone, 1-phenyl-4-methyl-3-pyrazolidone, 1-phenyl-2- benzoyl-3-pyrazolidone, 1 phenyl 2 -1auroyl- 3-pyrazolidone, 1-phenyl-2-chloroacetyl-3-pyrazolidone, etc.

The concentration of auxiliary developing agents can be varied and, of course, no auxiliary developing agent need be employed unless so desired. Useful concentrations of auxiliary developing agents vary from about 0.01 to about 2.0 mole per mole of 1RD developing agent compound. Depending upon the particular auxiliary developing agent employed, larger or smaller quantities can be used.

The iodo developers of our invention can be used in emulsions intended for use in diffusion transfer processes which utilize the undeveloped silver halide in the nonimage areas of the negative to form a positive by dissolving the undeveloped silver halide and precipitating it on a receiving layer in close proximity to the original silver halide emulsion layer. Such processes are described in Rott U.S. Patent 2,352,014, issued June 20, 1944, and Land U.S. Patents 2,584,029, issued January 29, 1952; 2,698,236, issued December 28, 1954, and 2,543,181, issued February 27, 1951; and Yackel et al. U.S. Patent 3,020,155, issued February 6, 1962. They may also be used in color transfer processes which utilize the diffusion transfer of an imagewise distribution of developer, coupler or dye, from a light-sensitive layer to a second layer, while the two layers are in close proximity to one another. Color processes of this type are described in Land U.S. Patents 2,559,643, issued July 10, 1951, and 2,698,798, issued January 4, 1955; Land and Rogers Belgian Patents 554,933 and 554,934, granted August 12, 1957; International Polaroid Belgian Patents 554,212, granted July 16, 1957, and 554,935, granted August 12, 1957; Yutzy U.S. Patent 2,756,142, granted July 24, 1956, and Whitmore and Mader U.S. Patent application Serial No. 734,141, filed May 9, 1958 and now abandoned. They may also be used in emulsions intended for use in a monobath process such as described in Haist et al. U.S. Patent 2,875,048, issued February 24, 1959, and in web-type processes, such as the one described in Tregillus et al. U.S. Patent application Serial No. 835,473, filed August 24, 1959, now U.S. Patent No. 3,179,517.

Of course, the activator solutions which are used in our invention are stable for extended periods of time and are not subject to the harmful decomposition reactions so common to conventional photographic developing solutions when these developing solutions are stored for extended periods of time. No special precautions are required to prevent oxidation of the activator solutions since they are inherently quite stable. If desired, the activator compounds can be incorporated in a carrier, such as gelatin and coated in contact with the photographic silver halide emulsion layer which contains the development precursors of our invention. After exposure, the development can be effected merely by heating the photographic emulsion layer to a temperature suflicient to release Water, which may be present in the support or in a separate layer in the photographic element. This water then dissolves the activator compounds from the hydrophilic colloid layers and takes them into the photographic halide emulsion layer where the emulsion is effected.

The elevated temperatures from about 95-150 C. are usually suflicient to effect development in this manner. If desired, additional moisture can be added by spraying steam upon the sensitive surface of the photographic element.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A photographic element comprising a support and a photographic silver halide emulsion layer comprising a water-permeable hydrophilic colloid layer containing a compound represented by the following general formula:

l 0 Rs wherein R R R and R each represent a member selected from the class consisting of a hydrogen atom, an iodine atom, alkyl groups having about 1-20 carbon atoms, OH, amine and aryl groups provided at least one of the substituents R R R or R must be iodine and one of the other substituents, R R R or R must be a group other than hydrogen and R and R represent a member selected from the class consisting of a hydrogen atom, and an alkaline splittable masking group.

2. A photographic element comprising a support and a photographic silver halide emulsion layer, and integral with said photographic element a water-permeable hydrophilic colloid layer containing a compound represented by the following general formula:

wherein R R R and R each represent a member selected from the class consisting of a hydrogen atom, an iodine atom, alkyl groups having about 12O carbon atoms, OH, amine, and aryl groups provided at least one of the substituents, R R R or R must be iodine and one of the other substituents, R R R or R must be a group other than hydrogen, and R and R represent a member selected from the class consisting of a hydrogen atom, and an alkaline splittable masking group.

3. A photographic element comprising a paper support and a photographic silver halide emulsion layer comprising a water-permeable hydrophilic colloid layer containing a silver halide developer and a compound representedby the following general formula:

wherein R R R and R each represent a member selected from the class consisting of a hydrogen atom, an iodine atom, alkyl groups having about l-20 carbon atoms, OH, amine and aryl groups provided at least one of the substituents, R R R or R must be iodine and one of the other substituents, R R R or R must be a group other than hydrogen, and R and R represent a member selected from the class consisting of a hydrogen atom, and an alkaline splittable masking group.

4. A photographic element comprising a support and a photographic silver halide emulsion layer comprising a water-permeable hydrophilic colloid layer containing a colloidal dispersion of a compound in tricresyl phosphate, said compound represented by the following general formula:

wherein R R R and R each represent a member selected from the class consisting of a hydrogen atom, an iodine atom, alkyl groups having about 1-20 carbon atoms, OH, amine and aryl groups provided at least one of the substituents, R R R or R must be iodine and one of the other substituents, R R R or R must be a group other than hydrogen, and R and R represent a member selected from the class consisting of a hydrogen atom, and an alkaline splittable masking group.

5. A process for forming a visible photographic image comprising developing an exposed photographic element comprising a support and a photographic silver halide emulsion layer, and integral with said photographic element, a water-permeable hydrophilic colloid layer containing a compound represented by the following general formula:

wherein R R R and R each represent a member selected from the class consisting of a hydrogen atom, an iodine atom, alkyl groups having about 120 carbon atoms, OH, amine and aryl groups provided at least one of the substituents, R R R or R must be iodine and one of the other substituents, R R R and R must be a group other than hydrogen, and R and R represent a member selected from the class consisting of a hydrogen atom, and an alkaline splittable masking group by imbibing throughout said photographic silver halide emulsion layer an aqueous alkaline solution containing suflicient alkali to give a pH of at least about 9.0.

6. A process for forming a visible photographic image comprising developing an exposed photographic element comprising a support having thereon a photographic silver halide gelatino emulsion layer containing a silver halide developer and a compound selected from the class of compounds represented by the following general formula:

wherein R R R and R each represent a member selected from the class consisting of a hydrogen atom, an iodine atom, alkyl groups having about 1-20 carbon atoms, OH, amine and aryl groups provided at least one of the substituents, R R R or R must be iodine and one of the other substituents, R R R or R must be a group other than hydrogen, and R and R represent a member selected from the class consisting of a hydrogen atom, and an alkaline splittable masking group, by imbibing throughout said photographic silver halide emulsion layer an aqueous alkaline solution containing suflicient alkali to give a pH of at least about 9.0.

7. A process for forming a visible photographic image comprising developing an exposed photographic element comprising a support and a photographic silver halide emulsion layer, and integral with said photographic element, a water-permeable, hydrophilic colloid layer containing a compound selected from the class of compounds represented by the following general formula:

wherein R R R and R each represent a member selected from the class consisting of a hydrogen atom, an iodine atom, alkyl groups having about 1-20 carbon atoms, OH, amine, and aryl groups provided at least one of the substituents, R R R or R must be iodine and' one of the other substituents, R R R or R must be a group other than hydrogen, and R and R represent a member selected from the class consisting of a hydrogen atom, and an alkaline splittable masking group, by imbibing throughout said photographic silver halide emulsion layer an aqueous alkaline solution containing a silver halide developer.

8. A photographic element as defined in claim 1 Wherein said compound is 2,6-diiodohydroquinone.

9. A photographic element as defined in claim 1 wherein said compound is 6-iodo-2,3,5-trimethyl hydroquinonel 10. A photographic element as defined in claim 1 wherein said compound is 2-iodo-5-pentadecyl hydroquinone.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Hanson, W. T.: The Chemistry of Developers, Amer. Phot., volume 36, January 1944.

Lee et al.: Superadditivity in Photographic Development by Substituted Hydroquinones Used With Phenidone, P.S.E., volume 6, Number 1, JanuaryFebruary 1962.

Mees, C. E. K.: The Theory of the Photographic Process, New York, The Macmillan Company, 1954, page 554.

NORMAN G. TORCHIN, Primary Examiner.

C. E. DAVIS, Assistant Examiner. 

5. A PROCESS FOR FORMING A VISIBLE PHOTOGRAPHIC IMAGE COMPRISING DEVELOPING AN EXPOSED PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT AND A PHOTOGRAPHIC SILVER HALIDE EMULSION LAYER, AND INTEGRAL WITH SAID PHOTOGRAPHIC ELEMENT, A WATER-PERMEABLE HYDROPHILIC COLLOID LAYER CONTAINING A COMPOUND REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 